SQL Server: GROUP BY - ROLLUP clause

with tab as (
     select 2020 year_,  1 quarter_,  'A'  grp_1, 'X' grp_2,   7  val union all
     select 2020 year_,  1 quarter_,  'A'  grp_1, 'X' grp_2,   6  val union all
     select 2020 year_,  1 quarter_,  'A'  grp_1, 'Y' grp_2,   1  val union all
     select 2020 year_,  1 quarter_,  'A'  grp_1, 'Y' grp_2,   4  val union all
     --
     select 2020 year_,  2 quarter_,  'A'  grp_1, 'Y' grp_2,   6  val union all
     select 2020 year_,  2 quarter_,  'A'  grp_1, 'Y' grp_2,   5  val union all
     --
     select 2020 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   2  val union all
     select 2020 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   1  val union all
     select 2020 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   5  val union all
     --
     select 2020 year_,  4 quarter_,  'A'  grp_1, 'X' grp_2,   2  val union all
     select 2020 year_,  4 quarter_,  'A'  grp_1, 'X' grp_2,   2  val union all
     -------
     select 2020 year_,  1 quarter_,  'B'  grp_1, 'X' grp_2,   7  val union all
     select 2020 year_,  1 quarter_,  'B'  grp_1, 'X' grp_2,   6  val union all
     select 2020 year_,  1 quarter_,  'B'  grp_1, 'Z' grp_2,   1  val union all
     select 2020 year_,  1 quarter_,  'B'  grp_1, 'Z' grp_2,   4  val union all
     --
     select 2020 year_,  2 quarter_,  'B'  grp_1, 'X' grp_2,   6  val union all
     select 2020 year_,  2 quarter_,  'B'  grp_1, 'X' grp_2,   5  val union all
     select 2020 year_,  2 quarter_,  'B'  grp_1, 'X' grp_2,   8  val union all
     select 2020 year_,  2 quarter_,  'B'  grp_1, 'Z' grp_2,   5  val union all
     --
     select 2020 year_,  3 quarter_,  'B'  grp_1, 'Y' grp_2,   4  val union all
     select 2020 year_,  3 quarter_,  'B'  grp_1, 'Z' grp_2,   5  val union all
     select 2020 year_,  3 quarter_,  'B'  grp_1, 'Z' grp_2,   6  val union all
     --
     select 2020 year_,  4 quarter_,  'B'  grp_1, 'Y' grp_2,   2  val union all
     select 2020 year_,  4 quarter_,  'B'  grp_1, 'Y' grp_2,   2  val union all
 
     -------------------------------------------------------------------------
 
     select 2021 year_,  1 quarter_,  'A'  grp_1, 'X' grp_2,   6  val union all
     select 2021 year_,  1 quarter_,  'A'  grp_1, 'X' grp_2,   9  val union all
     select 2021 year_,  1 quarter_,  'A'  grp_1, 'Z' grp_2,   2  val union all
     --
     select 2021 year_,  2 quarter_,  'A'  grp_1, 'Y' grp_2,   6  val union all
     select 2021 year_,  2 quarter_,  'A'  grp_1, 'Y' grp_2,   5  val union all
     --
     select 2021 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   2  val union all
     select 2021 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   1  val union all
     select 2021 year_,  3 quarter_,  'A'  grp_1, 'Z' grp_2,   5  val union all
     --
     select 2021 year_,  4 quarter_,  'A'  grp_1, 'X' grp_2,   2  val union all
     select 2021 year_,  4 quarter_,  'A'  grp_1, 'X' grp_2,   2  val union all
     -------
     select 2021 year_,  1 quarter_,  'B'  grp_1, 'X' grp_2,   4  val union all
     select 2021 year_,  1 quarter_,  'B'  grp_1, 'X' grp_2,   5  val union all
     --
     select 2021 year_,  2 quarter_,  'B'  grp_1, 'Z' grp_2,   1  val union all
     select 2021 year_,  2 quarter_,  'B'  grp_1, 'Z' grp_2,   2  val union all
     select 2021 year_,  2 quarter_,  'B'  grp_1, 'Z' grp_2,   3  val union all
     --
     select 2021 year_,  3 quarter_,  'B'  grp_1, 'X' grp_2,   4  val union all
     select 2021 year_,  3 quarter_,  'B'  grp_1, 'Y' grp_2,   5  val union all
     select 2021 year_,  3 quarter_,  'B'  grp_1, 'Y' grp_2,   6  val union all
     --
     select 2021 year_,  4 quarter_,  'B'  grp_1, 'Z' grp_2,   2  val union all
     select 2021 year_,  4 quarter_,  'B'  grp_1, 'Y' grp_2,   2  val
)
select
-- grouping_id(year_, grp_1, grp_2) g,
   case grouping_id(grp_1, grp_2)
        when 1 then 'Total quarter, grp 1'
        when 3 then 'Total quarter'
   end " ",
   year_,
   quarter_,
   grp_1,
   grp_2,
   sum(val) sum_val
from
   tab
group by
   year_,
   quarter_,
   rollup(grp_1, grp_2)